WASHINGTON — The FBI probe of two men arrested in Amsterdam after suspicious items turned up in one of the men’s luggage is finding that they probably were not on a test run for a future terrorist attack, a U.S. official said Tuesday, casting doubt on earlier suggestions even as Dutch authorities held the pair on suspicion of conspiring to commit a terrorist act.

The U.S. does not expect to charge the men, a law enforcement official said. The two men, who were traveling to Yemen, did not know each other and were not traveling together, a U.S. government official said. The officials spoke to The Associated Press on condition of anonymity to discuss.

The Amsterdam arrests came at a time of heightened alert less than two weeks before the ninth anniversary of the Sept. 11, 2001, terrorist attacks. U.S. officials also have been concerned about Americans traveling to Yemen to join al-Qaeda.

U.S. officials earlier had said they were investigating whether the men had been conducting a dry run for a potential terrorist attack. But as the probe evolved, officials said that appeared unlikely.

Both of the detained men missed flights to Washington Dulles International Airport from Chicago, and United Airlines then booked them on the same flight to Amsterdam, the U.S. government official said. The men were sitting near each other on the flight but not together.

Transportation Security Administration screeners had discovered suspicious items in one man’s checked bag: a cellphone taped to a Pepto-Bismol bottle, multiple cellphones and watches taped together, a knife and a box cutter, according to another U.S. official who had been briefed on the investigation. None of the checked items violated U.S. security rules, so TSA allowed the man to fly.

The men were not on any U.S. terror watch lists, White House spokesman Robert Gibbs told CNN on Tuesday. Federal air marshals were on the flight from Chicago to Amsterdam, a law enforcement official said.

A Dutch prosecutor Tuesday did not address why the two men continued to be held even as U.S. officials cast doubt on the case.

Under Dutch law, they can be held for three days and 15 hours from the time of their arrest. After that period, they must be taken before an investigating judge if officials want their custody extended.

A U.S. official identified the men as Ahmed Mohamed Nasser al Soofi and Hezam al Murisi. Al Soofi had a Detroit address. Al Soofi had been living in Tuscaloosa, Ala.

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